The Upper Permian Sedimentary Facies in Sichuan Basin and Their Tectonic Controls

The Late Permian secimentary facies in eastern Sichuan and western Hubei show a complete range of facies types, and seven facies and eight subfacies have preliminarily been recognized, such as coastal swamp, tidal flat, bay, shelf, organic reef; shelf margin-slope and basin. In this paper, the features and the temporal and spatial distribution of the five facies and subfacies are outlined, thus resulting in the establishment of facies model for the succession. The Upper Permian in the area displays four transgressive and regressive cycles from which the lithologic members of the sections have been distinguished and correlated regionally. Eight palaeogeographic maps have been constructed. The evolution of the Late Permian sedimentary facies in various areas may be divided into four modes: transgressive, regressive, wavy and/or gently wavy. The differences of the evolutionary features indicate that the Late Permian tectonic movement in the area is characterized by differential uplift and subsidence of fault blocks. The occurrence of Upper Permian organic reefs from eastern Sichuan and western Hubei are evidently controlled by tectonics: Jiantianba Reef in Lichuan, Hubei, a type of barrier reef, occurs on the flank of the uplifted block within the conjunctive zone between the two adjacent blocks. Taiyun Reef from Fengdu, Sichuan is confined to the East Sichuan Block. Honghua Reef from Kaixian, Sichuan, a type of patch reef derived from a barrier reef, is aligned from east to west and becomes smaller and smaller in the scale of the reef bodies. It is distributed over the fault uplift in front of the Daba Mountains.